This series is dependent upon "refactor Kconfig to consolidate KEXEC and CRASH options". https://lore.kernel.org/lkml/20230626161332.183214-1-eric.devolder@xxxxxxxxxx/ Once the kdump service is loaded, if changes to CPUs or memory occur, either by hot un/plug or off/onlining, the crash elfcorehdr must also be updated. The elfcorehdr describes to kdump the CPUs and memory in the system, and any inaccuracies can result in a vmcore with missing CPU context or memory regions. The current solution utilizes udev to initiate an unload-then-reload of the kdump image (eg. kernel, initrd, boot_params, purgatory and elfcorehdr) by the userspace kexec utility. In the original post I outlined the significant performance problems related to offloading this activity to userspace. This patchset introduces a generic crash handler that registers with the CPU and memory notifiers. Upon CPU or memory changes, from either hot un/plug or off/onlining, this generic handler is invoked and performs important housekeeping, for example obtaining the appropriate lock, and then invokes an architecture specific handler to do the appropriate elfcorehdr update. Note the description in patch 'crash: change crash_prepare_elf64_headers() to for_each_possible_cpu()' and 'x86/crash: optimize CPU changes' that enables further optimizations related to CPU plug/unplug/online/offline performance of elfcorehdr updates. In the case of x86_64, the arch specific handler generates a new elfcorehdr, and overwrites the old one in memory; thus no involvement with userspace needed. To realize the benefits/test this patchset, one must make a couple of minor changes to userspace: - Prevent udev from updating kdump crash kernel on hot un/plug changes. Add the following as the first lines to the RHEL udev rule file /usr/lib/udev/rules.d/98-kexec.rules: # The kernel updates the crash elfcorehdr for CPU and memory changes SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" With this changeset applied, the two rules evaluate to false for CPU and memory change events and thus skip the userspace unload-then-reload of kdump. - Change to the kexec_file_load for loading the kdump kernel: Eg. on RHEL: in /usr/bin/kdumpctl, change to: standard_kexec_args="-p -d -s" which adds the -s to select kexec_file_load() syscall. This kernel patchset also supports kexec_load() with a modified kexec userspace utility. A working changeset to the kexec userspace utility is posted to the kexec-tools mailing list here: http://lists.infradead.org/pipermail/kexec/2023-May/027049.html To use the kexec-tools patch, apply, build and install kexec-tools, then change the kdumpctl's standard_kexec_args to replace the -s with --hotplug. The removal of -s reverts to the kexec_load syscall and the addition of --hotplug invokes the changes put forth in the kexec-tools patch. Regards, eric --- v24: 28jun2023 - Rebased onto 6.4.0 - Included Documentation/ABI/testing entries for the new sysfs crash_hotplug attributes, per Greg Kroah-Hartman. - Refactored drivers/base/cpu|memory.c to use the .is_visible() method for attributes, per Greg Kroah-Hartman. - Retained all existing Acks and RBs as the few changes as a result of Greg's requests were trivial. v23: 12jun2023 https://lore.kernel.org/lkml/20230612210712.683175-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.4.0-rc6 - Refactored Kconfig, per Thomas. See series: https://lore.kernel.org/lkml/20230612172805.681179-1-eric.devolder@xxxxxxxxxx/ - Reworked commit messages to conform to style, per Thomas. - Applied Baoquan He Acked-by to kexec_load() patch. - Applied Hari Bathini Acked-by for the series. - No code changes. v22: 3may2023 https://lore.kernel.org/lkml/20230503224145.7405-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.3.0 - Improved support for kexec_load(), per Hari Bathini. See "crash: hotplug support for kexec_load()" which is the only change to this series. - Applied Baoquan He's Acked-by for all other patches. v21: 4apr2023 https://lkml.org/lkml/2023/4/4/1136 https://lore.kernel.org/lkml/20230404180326.6890-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.3.0-rc5 - Additional simplification of indentation in crash_handle_hotplug_event(), per Baoquan. v20: 17mar2023 https://lkml.org/lkml/2023/3/17/1169 https://lore.kernel.org/lkml/20230317212128.21424-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.3.0-rc2 - Defaulting CRASH_HOTPLUG for x86 to Y, per Sourabh. - Explicitly initializing image->hp_action, per Baoquan. - Simplified kexec_trylock() in crash_handle_hotplug_event(), per Baoquan. - Applied Sourabh's Reviewed-by to the series. v19: 6mar2023 https://lkml.org/lkml/2023/3/6/1358 https://lore.kernel.org/lkml/20230306162228.8277-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.2.0 - Did away with offlinecpu, per Thomas Gleixner. - Changed to CPUHP_BP_PREPARE_DYN instead of CPUHP_AP_ONLINE_DYN. - Did away with elfcorehdr_index_valid, per Sourabh. - Convert to for_each_possible_cpu() in crash_prepare_elf64_headers() per Sourabh. - Small optimization for x86 cpu changes. v18: 31jan2023 https://lkml.org/lkml/2023/1/31/1356 https://lore.kernel.org/lkml/20230131224236.122805-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.2.0-rc6 - Renamed struct kimage member hotplug_event to hp_action, and re-enumerated the KEXEC_CRASH_HP_x items, adding _NONE at 0. - Moved to cpuhp state CPUHP_BP_PREPARE_DYN instead of CPUHP_AP_ONLINE_DYN in order to minimize window of time CPU is not reflected in elfcorehdr. - Reworked some of the comments and commit messages to offer more of the why, than what, per Thomas Gleixner. v17: 18jan2023 https://lkml.org/lkml/2023/1/18/1420 https://lore.kernel.org/lkml/20230118213544.2128-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.2.0-rc4 - Moved a bit of code around so that kexec_load()-only builds work, per Sourabh. - Corrected computation of number of memory region Phdrs needed when x86 memory hotplug is not enabled, per Baoquan. v16: 5jan2023 https://lkml.org/lkml/2023/1/5/673 https://lore.kernel.org/lkml/20230105151709.1845-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.2.0-rc2 - Corrected error identified by Baoquan. v15: 9dec2022 https://lkml.org/lkml/2022/12/9/520 https://lore.kernel.org/lkml/20221209153656.3284-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.1.0-rc8 - Replaced arch_un/map_crash_pages() with direct use of kun/map_local_pages(), per Boris. - Some x86 changes, per Boris. v14: 16nov2022 https://lkml.org/lkml/2022/11/16/1645 https://lore.kernel.org/lkml/20221116214643.6384-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.1.0-rc5 - Introduced CRASH_HOTPLUG Kconfig item to better fine tune compilation of feature components, per Boris. - Removed hp_action parameter to arch_crash_handle_hotplug_event() as it is unused. v13: 31oct2022 https://lkml.org/lkml/2022/10/31/854 https://lore.kernel.org/lkml/20221031193604.28779-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.1.0-rc3, which means converting to use the new kexec_trylock() away from mutex_lock(kexec_mutex). - Moved arch_un/map_crash_pages() into kexec.h and default implementation using k/unmap_local_pages(). - Changed more #ifdef's into IS_ENABLED() - Changed CRASH_MAX_MEMORY_RANGES to 8192 from 32768, and it moved into x86 crash.c as #define rather Kconfig item, per Boris. - Check number of Phdrs against PN_XNUM, max possible. v12: 9sep2022 https://lkml.org/lkml/2022/9/9/1358 https://lore.kernel.org/lkml/20220909210509.6286-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.0-rc4 - Addressed some minor formatting items, per Baoquan v11: 26aug2022 https://lkml.org/lkml/2022/8/26/963 https://lore.kernel.org/lkml/20220826173704.1895-1-eric.devolder@xxxxxxxxxx/ - Rebased onto 6.0-rc2 - Redid the rework of __weak to use asm/kexec.h, per Baoquan - Reworked some comments and minor items, per Baoquan v10: 21jul2022 https://lkml.org/lkml/2022/7/21/1007 https://lore.kernel.org/lkml/20220721181747.1640-1-eric.devolder@xxxxxxxxxx/ - Rebased to 5.19.0-rc7 - Per Sourabh, corrected build issue with arch_un/map_crash_pages() for architectures not supporting this feature. - Per David Hildebrand, removed the WARN_ONCE() altogether. - Per David Hansen, converted to use of kmap_local_page(). - Per Baoquan He, replaced use of __weak with the kexec technique. v9: 13jun2022 https://lkml.org/lkml/2022/6/13/3382 https://lore.kernel.org/lkml/20220613224240.79400-1-eric.devolder@xxxxxxxxxx/ - Rebased to 5.18.0 - Per Sourabh, moved crash_prepare_elf64_headers() into common crash_core.c to avoid compile issues with kexec_load only path. - Per David Hildebrand, replaced mutex_trylock() with mutex_lock(). - Changed the __weak arch_crash_handle_hotplug_event() to utilize WARN_ONCE() instead of WARN(). Fix some formatting issues. - Per Sourabh, introduced sysfs attribute crash_hotplug for memory and CPUs; for use by userspace (udev) to determine if the kernel performs crash hot un/plug support. - Per Sourabh, moved the code detecting the elfcorehdr segment from arch/x86 into crash_core:handle_hotplug_event() so both kexec_load and kexec_file_load can benefit. - Updated userspace kexec-tools kexec utility to reflect change to using CRASH_MAX_MEMORY_RANGES and get_nr_cpus(). - Updated the new proposed udev rules to reflect using the sysfs attributes crash_hotplug. v8: 5may2022 https://lkml.org/lkml/2022/5/5/1133 https://lore.kernel.org/lkml/20220505184603.1548-1-eric.devolder@xxxxxxxxxx/ - Per Borislav Petkov, eliminated CONFIG_CRASH_HOTPLUG in favor of CONFIG_HOTPLUG_CPU || CONFIG_MEMORY_HOTPLUG, ie a new define is not needed. Also use of IS_ENABLED() rather than #ifdef's. Renamed crash_hotplug_handler() to handle_hotplug_event(). And other corrections. - Per Baoquan, minimized the parameters to the arch_crash_ handle_hotplug_event() to hp_action and cpu. - Introduce KEXEC_CRASH_HP_INVALID_CPU definition, per Baoquan. - Per Sourabh Jain, renamed and repurposed CRASH_HOTPLUG_ELFCOREHDR_SZ to CONFIG_CRASH_MAX_MEMORY_RANGES, mirroring kexec-tools change by David Hildebrand. Folded this patch into the x86 kexec_file_load support patch. v7: 13apr2022 https://lkml.org/lkml/2022/4/13/850 https://lore.kernel.org/lkml/20220413164237.20845-1-eric.devolder@xxxxxxxxxx/ - Resolved parameter usage to crash_hotplug_handler(), per Baoquan. v6: 1apr2022 https://lkml.org/lkml/2022/4/1/1203 https://lore.kernel.org/lkml/20220401183040.1624-1-eric.devolder@xxxxxxxxxx/ - Reword commit messages and some comment cleanup per Baoquan. - Changed elf_index to elfcorehdr_index for clarity. - Minor code changes per Baoquan. v5: 3mar2022 https://lkml.org/lkml/2022/3/3/674 https://lore.kernel.org/lkml/20220303162725.49640-1-eric.devolder@xxxxxxxxxx/ - Reworded description of CRASH_HOTPLUG_ELFCOREHDR_SZ, per David Hildenbrand. - Refactored slightly a few patches per Baoquan recommendation. v4: 9feb2022 https://lkml.org/lkml/2022/2/9/1406 https://lore.kernel.org/lkml/20220209195706.51522-1-eric.devolder@xxxxxxxxxx/ - Refactored patches per Baoquan suggestsions. - A few corrections, per Baoquan. v3: 10jan2022 https://lkml.org/lkml/2022/1/10/1212 https://lore.kernel.org/lkml/20220110195727.1682-1-eric.devolder@xxxxxxxxxx/ - Rebasing per Baoquan He request. - Changed memory notifier per David Hildenbrand. - Providing example kexec userspace change in cover letter. RFC v2: 7dec2021 https://lkml.org/lkml/2021/12/7/1088 https://lore.kernel.org/lkml/20211207195204.1582-1-eric.devolder@xxxxxxxxxx/ - Acting upon Baoquan He suggestion of removing elfcorehdr from the purgatory list of segments, removed purgatory code from patchset, and it is signficiantly simpler now. RFC v1: 18nov2021 https://lkml.org/lkml/2021/11/18/845 https://lore.kernel.org/lkml/20211118174948.37435-1-eric.devolder@xxxxxxxxxx/ - working patchset demonstrating kernel handling of hotplug updates to x86 elfcorehdr for kexec_file_load RFC: 14dec2020 https://lkml.org/lkml/2020/12/14/532 https://lore.kernel.org/lkml/b04ed259-dc5f-7f30-6661-c26f92d9096a@xxxxxxxxxx/ - proposed concept of allowing kernel to handle hotplug update of elfcorehdr --- Eric DeVolder (10): drivers/base: refactor cpu.c to use .is_visible() drivers/base: refactor memory.c to use .is_visible() crash: move a few code bits to setup support of crash hotplug crash: add generic infrastructure for crash hotplug support kexec: exclude elfcorehdr from the segment digest crash: memory and CPU hotplug sysfs attributes x86/crash: add x86 crash hotplug support crash: hotplug support for kexec_load() crash: change crash_prepare_elf64_headers() to for_each_possible_cpu() x86/crash: optimize CPU changes .../ABI/testing/sysfs-devices-memory | 8 + .../ABI/testing/sysfs-devices-system-cpu | 8 + .../admin-guide/mm/memory-hotplug.rst | 8 + Documentation/core-api/cpu_hotplug.rst | 18 + arch/x86/Kconfig | 3 + arch/x86/include/asm/kexec.h | 18 + arch/x86/kernel/crash.c | 140 ++++++- drivers/base/cpu.c | 83 +++- drivers/base/memory.c | 91 ++++- include/linux/crash_core.h | 9 + include/linux/kexec.h | 63 +++- include/uapi/linux/kexec.h | 1 + kernel/Kconfig.kexec | 35 ++ kernel/crash_core.c | 355 ++++++++++++++++++ kernel/kexec.c | 5 + kernel/kexec_core.c | 6 + kernel/kexec_file.c | 187 +-------- kernel/ksysfs.c | 15 + 18 files changed, 819 insertions(+), 234 deletions(-) -- 2.31.1
